The following relates to the lighting arts. It especially relates to LED-based lighting assemblies including LED-based lighting assembly modules for flexible lighting strips. However, the following will also find application in conjunction with lighting assemblies, methods for manufacturing lighting assemblies, electronics associated with lighting assemblies, and applications employing lighting assemblies, such as illumination, illuminated channel lettering, border lighting, and so forth.
Light emitting diodes (LEDs) are used in lighting assemblies, where they have certain advantages of incandescent, fluorescent, and other lighting technologies. For example, LEDs are compact, durable, relatively energy efficient, operable at low voltage, and so forth. In a typical arrangement, one or more LEDs are attached to a printed circuit board and are connectable with a power source via circuitry of the printed circuit board. If the power source is not directly compatible with the LEDs (for example, a 110 VAC house voltage applied to LEDs that typically operate at a few volts DC) then the printed circuit can also include power conditioning circuitry that converts the power to a form amenable to driving the LEDs. Alternatively or additionally, an AC/DC converter, DC power supply, or other power conditioning component can be interposed between the 110 VAC and the printed circuit board.
High brightness LEDs in lighting assemblies typically operate at relatively low voltage but relatively high current. The total electrical power input to a commercial high-brightness LEDs is typically at the level of hundreds of milliwatts to a few watts per LED. Accordingly, efficient removal of generated heat is a concern.
One known approach for removing excess heat generated during LED operation is the use of metal heat sinks. Luxeon® LED emitters (available from LumiLeds Lighting, LLC, San Jose, Calif.) and some other commercial high-brightness LEDs include a metal heat slug on which the semiconductor chip is attached or otherwise thermally contacts. In order to maintain a compact profile, the metal heat slug of the LED cannot be very large, and is typically intended to conduct heat to a larger external heat sink that provides dissipation of heat to the surrounding ambient. Accordingly, the LED is mounted on a metal heat sink. In some lighting assemblies, the metal heat sink is incorporated into the printed circuit board. Such a composite board is commonly referred to as a metal core printed circuit board.
A metal heat sink adds substantial cost and weight to the lighting assembly, and may be relatively inefficient at dissipating heat. Common heat sink metals such as copper have high density, making heat sinks massive. Moreover, the surface area for dissipation of heat to the ambient corresponds to the surface area of the metal heat sink. To achieve good thermal coupling with the ambient, metal heat sinks typically include fins or other radiating structures, which increases weight and bulk of the heat sink. Optionally, forced air convection generated by a fan can be used to increase heat transfer to the ambient, or active water cooling can be incorporated. However, these approaches add substantial cost, bulk, and complexity to the lighting assembly.
Another problem with metal heat sinks is that the thermal pathway from the LED to the metal heat sink is of limited area. If the LED is mounted by mounting leads, the thermal pathway may be limited to the area of the leads. In some lighting assemblies, a thermally conductive underfill material is disposed between the LED and the metal core printed circuit board to facilitate heat transfer. Such underfilling, especially when used in conjunction with an LED having an integral heat slug, substantially increases the thermal pathway area, but generally cannot increase the thermal pathway area substantially beyond the overall footprint area of the LED.
In some other approaches, the LEDs are potted using a thermally conductive material. For example, Roney et al., U.S. Pat. No. 5,632,551 and Roney et al., U.S. Pat. No. 5,528,474 disclose potted LED assemblies. Typically, the potting material is a two-component epoxy or other two-component potting material that is combined or mixed as it is applied to the lighting assembly, and is then cured. Polycondensation, addition reactions, or other chemical processes occurring in the mixture during curing causes solidification of the potting material around the LEDs of the lighting assembly.
Potting can provide a larger thermal contact area between the LED and the heat sink, but has certain other disadvantages. A container or housing is typically required to retain the potting material in its liquid form during solidification. The container or housing adds weight and bulk to the lighting assembly, and may be problematic for certain low-profile lighting assemblies. Moreover, the potting material typically does not have enough thermal mass by itself to dissipate heat generated by the LEDs. Accordingly, potting is commonly employed in LED-based lighting assemblies in conjunction with a metal heat sink.
The following contemplates improved apparatuses and methods that overcome the above-mentioned limitations and others.